Since polyimide resins are excellent in various characteristic properties such as mechanical strength, adhesiveness, solvent resistance, low-temperature resistance, heat resistance, flame retardance, electric insulating property and the like and have been in wide use for electric and electronic parts. Especially, the resins have been widely utilized as insulating films, protective films and flexible printed circuit boards of semiconductors, and substrates of heat-resistance adhesive tapes.
Where polyimide resins are employed as a resin varnish, the polyimide resin is dissolved in an organic solvent and the resulting solution is applied onto a substrate or the like and thermally treated to remove the solvent for curing. Alternatively, a polyamic acid that is a precursor of a polyamide resin may be dissolved in an organic solvent and coated onto a substrate or the like, and is thermally treated to remove the organic solvent and simultaneously to permit the imidization reaction to proceed for curing. In either case, the organic solvent has to be evaporated during operations and thus, local exhaust equipment or the like is essential. Additionally, there are concerns about environmental burdens. On the other hand, where a polyimide resin is used as a film, no organic solvent is needed and thus, no provision such as of local exhaust equipment is necessary, with no concerns about environmental burdens. In this connection, however, such a film has the problem in that there is no degree of freedom over thickness in use and the film is unsuited for applications that require fluidity.
In case where it is desirable to use polyimide resins in the form of a coating liquid without use of solvents, there are required techniques of dilution with reactive diluents.
For instance, JP-A 2002-332305 and JP-A 2006-104447 set forth the use of an acrylic monomer as a reactive diluent in such techniques as mentioned above, which involves the problem in that the acrylic monomer is low in heat resistance, with the tendency to impede the physical properties of polyimide resins.
By the way, epoxy resins can be provided in a variety of forms including from liquid to tablet and cured products thereof are excellent in characteristic properties such as electric characteristics, heat resistance, adhesiveness, moisture proofing (water proofing) and the like. Hence, the epoxy resins have been widely used in the fields of electric and electronic parts, structural materials, adhesives, paints and the like. In recent years, however, adhesion reliability required for electronic materials have been very severe, for which the use of epoxy resins may not be always satisfactory. In such a case, the use of such polyimide resins as set out above can solve the above problem in many cases. Nevertheless, a current situation is such that there is no proper material or composition for use in applications satisfying solvent-free and liquid requirements.